This invention relates to a communication control system for use in a mobile radio telephone network.
A mobile radio telephone network of the type described, generally comprises a telephone line and a plurality of radio telephone sets. The radio telephone sets are movable in an area which is divided into a predetermined number of zones.
For the time being, it will be presumed that the area is within limits of a factory or in a head office of a corporation. In this case, the telephone line is a collection of subscriber lines extended from a central office to a private branch exchange of the factory or the head office. Alternatively, the telephone line is a collection of extension lines which are extended from the private branch exchange. Each radio telephone set may be a cordless telephone set.
A plurality of radio communication devices are assigned to the respective zones. It will be supposed merely for brevity of description that all radio telephone sets are alive, namely, capable of always carrying out communication, and are moving among the zones. Some of the radio telephone sets can use the radio communication device assigned to the zone in which the radio telephone sets in question are present at a time.
Between the telephone line and the radio communication devices, a control unit is connected to control communication between the telephone line and the radio communication devices. The control unit serves as a communication control system to which the present invention is directed.
A conventional communication control system has been considered by the assignees of the instant invention and includes a memory for memorizing, in correspondence to the radio telephone sets, location information signals indicative of the radio communication devices assigned to the zones in which the radio telephone sets are present at a time. Thus, the memory is used in memorizing the location information signals as a content of the memory.
When an arrival signal arrives at the telephone line to specify a specific or called telephone set among the radio telephone sets, the control unit selects one of the radio communication devices as a specific communication device with reference to the content of the memory. This one of the radio communication devices is indicated by one of the location information signals that is in correspondence to the specific telephone set. Then, the control unit sends the arrival signal as a call signal to the specific communication device for transmission to the specific telephone set. Responsive to the call signal, the specific telephone set transmits a response signal to the specific communication device for reception by the control unit when the specific telephone set is present in one of the zones that is assigned with the specific communication device.
When the specific telephone set is not present in the above-mentioned one of the zones, the specific telephone set can not receive the call signal. Therefore, the control unit can not receive the response signal. More specifically, the control unit can not receive the response signal when the specific telephone set moves from the above-mentioned one of the zones to a different one of the zones. It should be understood in this connection that the location information signal for the specific telephone set is kept untouched in the memory to indicate the specific communication device. When the control unit can not receive the response signal within a predetermined time after transmission of the call signal towards the specific telephone set, the control unit judges that the specific telephone set is out of position. At any rate, the conventional communication control system is incapable of transmitting the call signal to the specific telephone set when the specific telephone set is not present in one of the zones that is assigned with the specific communication device indicated by the location information signals.